Structural components for automobiles, for example, often are important from the point of view of safety and frequently are required to have specific deformation properties in the case of a crash. Such components must have greater yieldability at certain points and must be more resistant to deformation at other regions, even though they may be in the form of sheet bars, i.e. elongated members that may have different shapes or cross sections. In more general terms, such structural elements must have stronger and weaker regions to allow deformation energy to be dissipated in a defined manner. In spite of the fact that such bars or structural elements may have to have stronger and weaker regions, they nevertheless should be fabricated in one piece.
To produce structural components that are optimally matched for a crash situation, German patent document DE 100 49 660 A1 discloses a so-called patchwork sheet bar in which the basic sheet metal structure is reinforced at certain locations by reinforcing plates that are bonded to the basic structure to form a composite at those locations. The resulting patched composite can be heated to a temperature of about 800 to 850° C. and then subjected to a reshaping in the hot state and then, while being locked into the reshaped state is cooled in a defined manner with the reforming tool and thereby hardened. The production of the composite is however expensive and time-consuming as a result of the need to join the reinforcing plates to the basic sheet metal structure.
In addition to this patchwork method, DE 199 62 754 A1 discloses a method of flexible rolling a metal strip in which during the rolling process different wall thickness regions are formed on the strip. The strip with these regions of different wall thicknesses can then be cut to form components with the different wall thicknesses. To avoid temperature-based variations in the thickness and the longitudinal profile of the metal strip, during the rolling a compensation for the various temperature influences on the strip is effected to avoid deviations from the set-point thickness and/or set-point lengths of the individual strip segments at a predetermined final temperature of the strip. If the different thicknesses in the strip are characterized by markings in the middle strip, for exact positioning of the cut contours of the sheet bar products, this method can be used to produce such sheet bar products both as rectangular and as bars of other shapes in a reproducible manner. Nevertheless this method is not fully satisfactory for the production of elongated structural components that are to have optimal deformation properties as parts of a motor vehicle body or chassis in the case of a crash.